1. Field of the Invention
The present invention relates to an optical disc driving system, and more particularly, to a method and apparatus for compensating for eccentricity of an optical recording medium during data recording/reproducing.
2. Description of the Related Art
In general, disc eccentricity is the major disturbance component in an optical disc servo system.
FIGS. 1A through 1D illustrate track shapes of a non-eccentric disc and an eccentric disc and waveforms of tracking error signals detected for the two discs.
FIG. 1A shows a normal optical disc that has no eccentricity component and FIG. 1B illustrates the waveform of the tracking error signal detected for the non-eccentric disc of FIG. 1A. FIG. 1C shows an optical disc that has an eccentricity component and FIG. 1D illustrates the waveform of the tracking error signal detected for the eccentric disc of FIG. 1C.
Typically, optical discs should be manufactured without any eccentricities. However, due to technical problems in disc manufacturing such as poor manufacturing conditions, most optical discs have eccentricity components as shown in FIG. 1C. In practice, a specific amount of eccentricity is allowed when a recording format of an optical disc is determined. In the case of compact discs (CDs), an eccentricity of maximum 280 μm is allowed. If a disc is eccentric, an eccentricity component due to the eccentricity of the disc can be identified in a disc tracking error signal, as shown in FIG. 1D. As a result, optical disc reproducing apparatuses cannot approximately control a tracking operation due to such eccentricity components. Thus, disc eccentricity should be compensated for.
FIG. 2 is a block diagram of a conventional optical disc driving apparatus having an eccentricity compensating function.
First, a radio frequency (RF) amplifying unit 230 amplifies an RF signal read by a pickup 220 and detects a tracking error signal and a focusing error signal from the amplified RF signal. A focusing servo unit 240 receives the focusing error signal detected by the RF amplifying unit 230 and generates a focusing servo control signal. A tracking servo unit 250 receives the tracking error signal detected by the RF amplifying unit 230 and generates a tracking servo control signal. A focus actuator 222 in the pickup 220 causes a laser beam emitted from the pickup 220 to be focused onto a disc 210 according to the focusing servo control signal generated by the focusing servo unit 240. A tracking actuator 224 in the pickup 220 causes the laser beam to follow tracks of the disc 210 according to the tracking servo control signal generated by the tracking servo unit 250. The RF amplifying unit 230 amplifies a recording signal obtained from the disc 210 in accordance with the focusing error signal and the tracking error signal. The recording signal is transmitted to a data processor (not shown) and the data processor outputs an audio signal or a video signal after performing an error correction operation. An eccentricity extracting unit 280 extracts eccentricity data corresponding to the tracking error signal of one period that is generated by the tracking servo unit 250. A memory 290 stores the eccentricity data extracted by the eccentricity extracting unit 280. An adder 270 adds the eccentricity data stored in the memory 290 to the tracking error signal during every sampling period, thereby compensating for the eccentricity of the disc 210.
However, the conventional optical disc driving apparatus of FIG. 2 is disadvantageous in that disturbance components such as disc defects are added to the original eccentricity component and have a negative influence upon an overall servo control.